A food web is a system of interlocking and interdependent food chains.
A food chain is a hierarchical series of organisms each dependent on the next as a source of food.
Basically, the difference of the two is that a food web contains multiple different species in the same level that eat the animal below it's status. A food chain is one after the other.
Answer: -
Organic compounds consisting of only carbon atoms and hydrogen atoms are known as hydrocarbons.
Hydrocarbons are used by us for mainly as a source of energy. Hydrocarbons make up gasoline which is used as fuel in automobiles.
Hydrocarbons depending on the type of unsaturation can be of three types - alkanes, alkenes and alkynes.
The answer you are looking for is water.